Generally, electronic devices such as a liquid crystal display, a semiconductor device, or the like, are manufactured by forming patterns of multiple layers on a substrate. In order to form these patterns, a photolithography process has been mainly used up to now. However, the photolithography process manufactures predetermined pattern masks and repeats a chemical etching process and a stripping process, such that the manufacturing process is complicated and a large amount of chemical wastes harmful to environment occur. This increases manufacturing costs, thereby degrading competitiveness of products. As a new method of forming patterns in order to solve the problems of the photolithography process, a roll printing method using a printing roll has been proposed.
Although there are various roll printing methods, a gravure printing method and a reverse offset printing method may be largely classified.
The gravure printing, which is a printing method that performs printing by covering ink on a concave plate and scratching extra ink, has been known as a method suitable for printing of various fields such as publication, packaging, cellophane, vinyl, polyethylene, or the like. A study to apply the gravure printing method to manufacturing of active devices or circuit patterns used for display devices has been conducted. Since the gravure printing transfer ink to the substrate by using a transfer roll, the patterns may be formed by one-time transfer by using the transfer roll corresponding to an area of the desired display device even in the case of a large-area display device. The gravure printing forms the ink patterns for resist on the substrate and may be used to pattern various patterns of display devices, for example, a TFT and a gate line and a data line connected to the TFT, a pixel electrode, a metal pattern for a capacitor, in the case of a liquid crystal display device.
However, the blanket used for general gravure printing is manufactured by casting a silicon-based resin into a solid master mold. The blanket manufactured as described above may have a limitation in manufacturing to have a uniform thickness and is difficult to mass produce as a pilot scale. Therefore, in order to precisely form fine patterns, the reverse offset printing method is mainly adopted.
The related art relating to the reverse offset printing method and the printing apparatus may refer to Documents 1 to 3 which was filed and published by an applicant of the present invention.
[Document 1] KR 10-2008-0090890 (Publication) Oct. 9, 2008
[Document 2] KR 10-2009-0020076 (Publication) Feb. 26, 2009
[Document 3] KR 10-2009-0003883 (Publication) Jan. 12, 2009
The entire contents of the specifications of Documents 1 to 3 are a description of the related art of the present invention and are described in the specification of the present invention.
FIG. 1 shows a section of a structure of a blanket according to the related art that is generally used for reverse offset printing. As shown in FIG. 1, the blanket according to the related art is configured to comprise a surface printing layer, a support layer, and a cushion layer and may further comprise a primer layer so as to secure adhesion between the layers. The surface printing layer is a layer that is directly covered with ink and transferred and is mainly manufactured by poly-di-methyl-siloxane (PDMS) and the support layer serves to support the surface printing layer and the cushion layer and is mainly manufactured by a PET film.
Further, the cushion layer serves to compensate the difference in thickness when the surface of the surface printing layer is not uniform and is mainly manufactured by the PDMS, similar to the surface printing layer.
The reverse offset printing method is a technology that is receiving considerable attention in view of saving costs and improving production speeds at the time of forming patterns, but requires a good quality of blanket so as to obtain a precise pattern. That is, since the quality of the patterns may depend on the characteristics of the blanket, the manufacturing of the high-quality printing blanket is a very important technical problem.
An example of factors to be considered so as to manufacture the excellent quality of blanket may comprise a) the thickness uniformity of the blanket, b) the hardness of the surface printing layer, c) presence or absence of foreign objects (bubble, dust, or the like) within the blanket, d) adhesion between the layers different from a base layer (base film), e) whether or not to introduce the cushion layer for process stability and performance degree, f) slip property of the cushion layer, g) the content of low-molecular silicon oil comprised in the surface printing layer, and h) a swelling ratio of ink and a solvent on the surface printing layer.
In particular, when the surface printing layer is swollen well by ink and a solvent, or the like, the time to dry the ink is long, such that the process waiting time is increased and the process margin is not good.